This invention relates to a combination thermionic-thermoelectric generator and more particularly to an apparatus and system which provides improved performance over prior known apparatus of this general type.
Thermionic and thermoelectric generators are well known in the art to be capable of generating electric currents by the application of heat to the devices. In the case of thermionic generators, current is created by the emission of electrons from a surface which has been heated sufficiently to allow the electron energy to overcome the potential barrier energy level of the surface. The basic theory of thermionic energy conversion is discussed in U.S. Pat. No. 2,980,819--Feaster issued Apr. 18, 1961. One difficulty known to exist with converters of this type is the relatively low usuable potential that can be developed unless a relatively large number of converters are cascaded in series with consequent increase in bulk and cost. Also, converters that give usuable current levels generally require extremely close interelectrode spacing between the emitters and collector electrodes, generally on the order of one millimeter. The difficulty in achieving and maintaining such close spacing, particularly at the high temperatures, e.g. 1200.degree. C. required to have usable electron emission, has limited the commercial usefulness of thermionic converters to highly specialized applications.
Thermoelectric converters, comprising a series of thermocouples, are also well known. In this device a current is generated by electron flow at the interface between the abutting surfaces of dissimilar materials maintained at different temperatures. By cascading a large number of these thermocouples, a thermopile can be produced which generates usable potential levels limited, in general, only by the practical length of the thermopile.
In the past, a number of combined thermionic and thermoelectric generators have been proposed in which the two types of devices are packaged together and electrically connected at a common therminal so that the heat applied to the package causes both generators to develop current outputs, usually at separate output terminals. Examples of such devices are shown and described in U.S. Pat. Nos. 3,189,765 and 3,430,079 issued June 15, 1965, and Feb. 25, 1969, respectively.
Despite the prior art which exists in this technology, it is believed that heretofore there has not existed a small, compack thermionic-thermoelectric generator apparatus capable of producing usable levels of current at usable potential levels. It is an object of this invention to provide a system embodying the improved apparatus with suitable switching circuits to furnish electrical current at usable potential levels to a load impedance.